Process for extracting metal values



March-7, 1967 R; A. RoNzlo ETAL 3,307,938 PROCESS FOR EXTRACTINGY METALVALUES Filed April 27, 1964 [PREcoNcEN RAT o OREI TRASH SCREENLLEAcHFEED RE PULPERI [HEAT TO a|cl AIR r g H o ABSQRBER TANK SZOZMIUTC)STEAM LEACHING ANKS 204 i 4 ltlsEw Z sT E A M -19: soRPT IONTANKSHVAGUUM PUMPHSO; RECOVE RY] AERATI ON TANKS AIR IMPURITIES ORGANICSTRIPPERI SPENT SLURRY TO TAILINGS STEAM CHARCOALIADSORPTION cm TANKSIZZSIERIES I c/mvzdumrr 00712 34111730 CHARCOAL ABSORPTION TANKS FIRSTSCREEN SER'ES (HIE NEW CHAR WASH CHARCOAL a CHAR'REGENERATION AIR CHARSTRIPPING ooLuMN FURNACE NH; J z STEAM 'MAGNESIUM SULFATEAPRECIPITATIONTANK INVENTORS I T R MAG.PH OS.ETC- FL E RICHARDAIRONZIO WAYNE C..HA2 ENW ENZO L.COLTRINARI ROBERT E. CUTHBERTSON W TTORNEY6 United StatesPatent 3,307,938 PROCESS FOR EXTRACTING METAL VALUES Richard A. Ronzio,Golden, Wayne C. Hazen, Wheatridge, Enzo L. Coltrinari, Arvada, andRobert E. Cuthbertson, Denver, Colo., assignors, by direct and mesneassignments, to American Metal Climax, Inc., New York, N.Y., acorporation of New York Filed Apr. 27, 1964, Ser. No. 363,007 32 Claims.(Cl. 75-103) The present invention relates to the treatment of mineralores and more particularly to a hydrometallurgical process forrecovering molybdenum from molybdenum bearing minerals.

As is known, the most important molybdenum ores contain molybdenite (Mand/or oxidized molybdenum that is associated with iron. The moreimportant deposits of ore, however, contain molybdenum largely as thesulfide, i.e., as M05 Although these molybdenum bearing ores seldomcarry more than 1% or so of the mineral, methods having been developedwhereby such ores are concentrated by flotation to produce a concentratecontaining 90% or more of the molybdenum disulfide. In such anoperation, however, that portion of the molybdenum found in the ore inan oxidized form is not flotated but appears in the tailings. As far asis known, no profitable commercial utilization has yet been made of suchoxidized form and it has been simply discarded.

The present invention resides primarily in the discovery of a profitableand economically feasible technique for extracting molybdenum from thoseoxidized portions of ores which heretofore have been considered acommercially impractical source. It has been recently discovered that inthe molybdenum ore deposits at Climax, Colorado, one of the largestdeposits of molybdenum in the world, the oxidized molybdenum isassociated with an iron oxide hydrate, goethite (Fe O -H O). Thisgoethite contains approximately 1.3 to 9.6% oxidized molybdenum byWeight. It is also apparently associated with other iron compounds suchas Jarosite (K Fe (OH) (SO and ferri-molybdite (FegMoO -XH O). As-aconsequence of this discovery, a feasible pro-concentration process hasbeen developed for concentrating the oxidized molybdenum values in thisore (approximately .14% molybdenum in a nonsulfide form) to a pointwhere it is commercially practical to extract them. This processoperates on the basis of concentrating iron oxide and since themolybdenum is dissolved therein there is thus produced a higherconcentration of molybdenum and consequently a reduction in the totalamount of material which will have to be handled through the remainderof the extraction process. This concentration can be effected byparticle size separation of the finely milled ore (since the ironcompounds are more friable they break into smaller particles than theremainder of the ore), by flotation, by magnetic separation, or by anycombination of these methods. By such methods it is possible to increasethe molybdenum concentration in this ore to approximately..30%(concentrations from .25% to .37% have been achieved). The ironconcentration in this concentrate would be approximately 3%, or roughlytenfold.

Considering the present process broadly, the pre-concentrated ore to beprocessed is preferably introduced in the form of a relatively high pulpdensity aqueous slurry (approximately 50% solids). This slurry is firstheated and then leached with a combination of sulfuric acid and gaseoussulfur dioxide to dissolve the iron and molybdenum compounds therein.The sulfur dioxide is then flashed off and the slurry is aerated. Theslurry is then passed through a series of activated charcoal adsorptiontanks where the molybdenum values are preferentially picked up by theactivated charcoal. The loaded charcoal "ice is then stripped with air,ammonia, and water to form ammonium molybdate solution. Undesirablephosphorous values may be precipitated as magnesium ammonium phosphateby adding magnesium sulfate to the solution. The ammonium molybdate maybe separated from the solution by crystallization and if desired may beconverted to molybdenum oxide of a greater than technical grade by acalcining operation.

It is therefore a-primary object of the present invention to provide animproved continuous process for economically extracting molybdenumvalues from ores containing molybdenum in oxidized forms.

A further object of this invention concerns the provision of an improvedprocess for economically leaching molybdenum values from molybdenumbearing ore. A related object concerns the provision of such a leachingprocess suitable for use on relatively high pulp density slurries, i.e.,in the order of 50% solids. Another related object concerns theprovision of such a leaching process which is relatively fast acting,thereby reducing the size of the leaching tanks required for a givenoutput capacity, as well as overall cycle time.

Yet another object of this invention resides in the provision of animproved process for preferentiallyextracting molybdenum values from aleach liquor containing dissolved iron and molybdenum values.

Another object resides in the provision of a novel com bined leachingand adsorption process for economically extracting high recovery amountsof molybdenum from ores containing the oxidized forms thereof.

-Another object of this invention concerns the provision of aunique-activated charcoal extraction process which possesses thedesirable characteristics of both cocurrent and countercurrent systemswithout being subject to the disadvantages thereof. A related objectresides in the provision of such a process which is operable upon aslurry, and specifically a high density slurry.

A further object resides in the provision of a novel charcoal strippingprocess which will yield molybdenum values of increased concentration,which has a heat of reaction operable to increase the speed of thestripping operation, and in which the primary stripping agent is.relatively inexpensive and easily recoverable for reuse.

Further objects, features, and advantages of this invention will becomeapparent from consideration of the following description, the appendedclaims, and the accompanying drawing in which there is shownschematically a fiow diagram of the present process.

The present invention will be described for examplary purposes onlyembodied in a detailed commercial process which has been found throughpilot plant and other studies to give very satisfactory results whenapplied to the presently obtained tailings from the commercialmolybdenite flotation plant now processing the molybdenum ore at Climax,Colorado.

The ore slurry from the pre-concentration process, ap-

' proximately .30% molybdenum, 50% solids, minus 65 mesh in size, andsubstantially neutral in pH, is first passed through a 35 mesh trashscreen to eliminate any trash. The slurry, which at this point isapproximately 4.4 C. because of the cold water used in thepre-concentration process, is fed, as it becomes available, into a surgetank from which it may be pumped continuously at a constant rate to theextraction system. Into this tank may also added, for reprocessing, thefiltration precipitate from the magnesium sulfate precipitation step, aswill be described in detail later. The' tank is under atmosphericpressure. The slurry may be pumped through heat exchangers which willincrease its temperature to approximately 31 C.

Heating is not essential at this point but since it is re-.

quired later in the process and since certain of the tailings from alater stage in the process are relatively hot (about 60 C.) thismaterial is used to preheat the slurry at this time. It is then fed intoan absorber tank into which also may be introduced a portion of the 50which is recovered from a later portion of the process. This S isslightly contaminated and dilute with air and moisture but may beeconomically utilized at this point because the slurry temperature isrelatively low and the gas therefor more soluble. The slurry may beagitated to aid absorption. This operation is continuous and the tank isat atmospheric pressure.

The slurry, which is still approximately 50% solids, is then fed througha series of leach tanks in which it is gently agitated at atmosphericpressure. A plurality of tanks are used to prevent any short circuitingof the slurry flow, and to provide flexibility of operation. Although apressure system would be faster it would not be as economical overallbecause of the considerably greater cost of pressure equipment. Inaddition, there may also be fouling as a result of the increasedformation of thionates. The operation is continuous and the rate of Howis such that the leach time is approximately 12 hours. To the first ofthese tanks is added sulfuric acid, gaseous sulfur dioxide and livesteam. To S0 is bubbled in at the bottom where the pressure and hencesolubility are the greatest. It has been found that 53 to 75 andpreferably about 72 pounds of 93% H SO per ton of dry ore, and 15 to 30and preferably about 20 pounds of 100% S0 per ton of dry ore give verysatisfactory results for ore of the type presently being mined atClimax, Colorado. The resulting pH of the solution should range between1.0 to 1.3 and is preferably approximately 1.2. The $0 ion concentrationshould range between to and is preferably approximately 10 grams perliter of solution, and the oxidation state (E.M.F.) of the solution isabout 200 to 250 mv. as measured with a platinum electrode withreference to a saturated calomel electrode. The steam serves to maintainleaching the temperature at approximately 60 C. It has been found thatleach temperatures of 60 to 70 C. give the best results, however at 70C. there is not enough of an improvement to economically justify thecost of the additional heat. Temperatures higher than 70 C. are notsatisfactory because of the decrease in S0 solubility.

Although it is not completely known in what exact forms the molybdenumexists in the leach liquor, because of the complex manner in which itsmany valence forms react, the liquor is predominantly iron in the formof ferrous sulfate, and the molybdenum is believed to be in the form ofmolybdenum blue, a complex acid colloid, and possibly some molybdate.Also there may be a small amount of phosphorous as phosphates, sulfur assulfates and thionates, and other normally encountered impurities. About95-96% of the molybdenum can be successfully leached by this operation.

Generally speaking, the leaching operation is an S0; leach. The processis greatly improved, however, by the addition of the H 80 for a numberof reasons. First, the acid greatly increases the speed of theoperation, the leaching time of S0 alone being as much as four timeslonger than with the combination of S0 and H 50 Second, it makes itpossible to obtain high leach extractions while operating in a very highdensity pulp. There factors substantially reduce the size and amount ofequipment required for leaching a given quantity of ore and for tailingsdisposal. Third, the H SO brings the pH level of the solution down to avalue which greatly enhances the later charcoal adsorption operation. Inthe absence of it the pH of the solution would increase to about 4 whenthe S0 was desorbed and as a consequence the ferric iron in the leachsolution would precipitate as a hydroxide, which would interfere withcharcoal adsorption. Fourth, if it is not used sulfites would be formedwhich would also interfere with charcoal adsorption since they tend tobe adsorbed before some of the molybdenum values. Fifth, it is believedthat the acidalso prevents the oxidation of some of the molybdenum blueto molybdate, which would not adsorb as well at a pH of 4. The H willnot Work satisfactorily alone because it will not dissolve more thanabout 60% of the iron. It is preferable that the S0 and H 80 be added tothe pulp in the same vessel since harmful scale was observed to form ifthe acid was added first.

The above specified quantities are those which have been found to do thejob the most economically overall. Sufficient S0 should be used tocompletely leach the iron and molybdenum values, with a minimum ofexcess. This amount may vary slightly with temperature, according toknown solubility principles. Also, for ores containing greaterquantities of iron and molybdenum proportionally greater amounts of S0should be used because there is more leaching to be done. For example,if the ore contained 20% molybdenum approximately 7 pounds S0 per ton ofore would be required, and if the ore contained .40% molybdenumapproximately 33 pounds of S0 per ton would be required. In actualpractice the quantity of H 50, should be sufiicient to bring the pHlevel down to an acceptable point (i.e., 1.0 to 1.3) and to speed thereaction time to where the process is the most economical. It has beenfound that the amount of acid required does not vary substantially withthe grade of ore, unless limestone or other alkaline materials arepresent in large quantities, in which case it should be increased.Although the use of additional quantities of S0 and H 50 would speedreaction time somewhat, it is wasteful of these materials and lesseconomical on the overall.

From the leaching tanks the slurry is pumped through a series ofdesorption tanks in which it is agitated a sufficient time to flash offthe S0 This may take anywhere from about 5 min. to 45 min. the exacttime not being critical. The process is continuous. These tanks aremaintained under a vacuum of approximately 6" Hg absolute and steam isinjected into the tanks to effect vaporization by heating the slurry.The temperature of the slurry in the tanks ranges from about 55 C. to 60C., from beginning to end, and the S0 concentration in the slurry outputis reduced to approximately 0.4 grams per liter of solution. If desired,the S0 flashed off in the desorption tanks may be recovered usingconventional techniques and re-used in the absorbing and leachingoperations discussed above. The portion of the S0 recovered in a lowgrade or slightly contaminated state would be used in the absorptionprocess. The

. oxidation state of the slurry issuing from the desorption tanks isapproximately 200 to-250 mv. as measured by a platinum electrode withreference to a saturated calomel electrode, and the pH is 1.3 to 1.8,and preferably about 1.5. Although this process might be performed byboiling the pulp, the high cost of the heat required makes such atechnique uneconomical.

The slurry is then fed through a barometric leg to a series of aerationtanks where it is agitated for a total of approximately 30 minutes whileair is blown upwardly through it. The tanks are under atmosphericpressure. This is a continuous process and it serves not only to removethe small remaining amount of S0 in the slurry, but more importantly tooxidize the slurry in a manner which greatly enhances the charcoaladsorption process. It has been found that the efficiency of thecharcoal adsorption process is greater with greater minus levels ofoxidation. Taking into account economical considerations, for charcoaladsorption the slurry should have an oxidation state (E.M.F.) ofapproximately 2S0 to 300 mv., and preferably about 270 mv., as measuredby a platinum electrode with reference to a saturated calomel electrode.Accordingly, air is added in an amount sufiicient to raise the oxidationlevel to this point. More air would give a more negative and a greaterpercent charcoal adsorption, up to a point (approximately -380 mv.),however it is too costly because of the air required and because itwould take a disproportionally longer time, thus requiring moreequipment and so on. The degree of oxidation of the solution appears tobe governed primarily by the ferric to ferrous ratio, rather than byoxidation of the molybdenum itself, and such oxidation can be effectedby either aerating the solution or adding ferric sulfate, although theformer is preferred. Even though there is ferric iron present it doesnot precipitate because the pH is about 1.5. The air does not seem toeffect the pH value. It has been found that the small amount of Soriginally present in the solution actually aids this oxidation process.

The slurry may then be fed through an organic stripper tank in which anyfloating oils or other organic materials may be skimmed off. If desired,these materials may be additionally processed for recovery of any of thedesired values therein.

The slurry (approximately 47% solids at this point) is now ready for theactivated charcoal adsorption operation. It would be advantageous to usea countercurrent flow charcoal adsorption system (the new charcoal andnew slurry flowing in opposite directions) so that the freshest charcoalwould be in contact with the weakest slurry. However, in order toaccomplish this it would be necessary to screen the charcoal from theslurry between each pair of adsorption tanks. Thus if seven tanks areused this would require six additional screens, which would not onlyrequire more equipment but would tend to break up the charcoal. coalmust eventually be separated from the ore slurry with a relativelycoarse screen. On the other hand, a cocurrent flow arrangement, unlikea countercurrent flow system, would be ineffective to build up a highmolybdenum loading on the charcoal unless the retention time was greatlyincreased. A high loading is advantageous since it reduces the quantityof material that must be handled in the stripping operation and thenumber of stripping operations required for a given quantity of charcoalto extract a given quantity of molybdenum. The present activatedcharcoal adsorption cycle achieves the advantages of both cocurrent andcountercurrent systems with a minimum amount of equipment and withoutthe disadvantages of either.

As can be seen from the flow sheet, in the present cycle the ore slurryand charcoal are cycled in a cocurrent fashion through a first series ofcharcoal adsorption tanks. The process is continuous and the tanks areat atmospheric pressure. Multiple tanks are used for the adsorptionoperation since it reduces the chance that some of the ore may shortcircuit the desired adsorption time period, which is preferably in theorder of 8 /2 hours in this series, and to provide flexibiilty. Duringthis period the ore is gently agitated by an impeller and draft tubearrangement. A small quantity of air may also be introduced into thetanks to maintain proper E.M.F. value, if it is found necessary. Theagitation need only be sufficient to keep the solids in suspension sinceexcessive agitation will break the charcoal. Steam is also introduced tothe first adsorption tank in the first series to maintain the slurry atapproximately 60 C. Generally, the higher the temperature the greaterthe adsorption efficiency, probably due to the increased mobility of themolybdenum molecules, at least up to approximately 120 C., at whichpoint the molybdenum will start to precipitate. However, 60 C. has beenfound to be the most economical on the overall. Increased pressures willalso increase adsorption efficiency, at least up to the point where theycause the slurry to reach 120 C., but are not economically practical inview of increased equipment and operating costs. Also they tend to causecorrosion problems. For the ore described, approximately 74% of thecharcoal and slurry flow is pumped from the first series of adsorptiontanks through a first screen (35 mesh) which separates the loadedcharcoal, which proceeds on to the stripping operation, from the slurry,which is re-cycled in This is undesirable because the charthe charcoaladsorption operation as will now be described.

Approximately 26%, or the balance, of the charcoal plus-slurry flow fromthe first series of charcoal adsorption tanks is bypassed from the firstscreen and fed in a cocurrent fashion through a second series ofcharcoal adsorption tanks. Also fed into this second series ofadsorption tanks is the slurry which was separated from the primary flowby the first screen. Here it is similarly agitated, but for only about 3/2 hours. The charcoaland-slurry flow from the second series ofadsorption tanks is then pumped through a second de-watering screenwhich separates the loaded charcoal from the spent slurry, which ispumped to tailings. The loaded charcoal from the second screen fiowsback into the first series of charcoal adsorption tanks for recycling.Thus, by virtue of this recycling operation it is possible to build up amolybdenum loading on the charcoal of 8% or more.

It has been found, taking into account flow rate, that adsorptionefiiciency varies with the number of cubic feet of charcoal per cubicfoot of adsorption tank. Based on this it has been found that verysatisfactory efiiciencies may 'be obtained using approximately 3 poundsof charcoal per cubic foot of total pulp. It has also been discoveredthat a charcoal loading of S to 15, and preferably 8, pounds ofmolybdenum per pounds of charcoal will yield a maximum amount ofadsorption within a practical period of time. If too long a period isused the charcoal wears, which is undersirable because it then becomesmore diflicult to separate, and because more equipment is required.Also, a portion of the charcoal is lost, thereby increasing the cost ofthe new charcoal added. For a given ore this loading may be obtained byregulating the proportion of the charcoal-plus-slurry flow which isbypassed from the first screen to the second series of adsorption tanks.The greater the amount bypassed the greater the charcoal loading. It isundesirable to bypass too much with a given amount of charcoal, within agiven period of time, since this will result in a wasteful flow ofunadsorbed molybdenum values to tailings. Different degrees of loadingmay better be achieved by varying the time of absorption.

Although the basic chemistry of the charcoal adsorption process is notwell understood, the charcoal does adsorb most (about 96%) of themolybdenum blue and other molyd-ates and only a very small amount of theother impurities. As discussed previously, it has been found that theefiiciency of' the adsorption operation is substantially affected by theoxidation level of the molybdenum solution. Experiments show that theadsorption process operates satisfactorily when the oxidation potential(E.M.F.) of the molybdenum solution has an value ranging from 220 mv. to300 mv. but is improved if the value is between 250 mv. and 300 mv., andpreferably -270, as measured by a platinum electrode with reference to asaturated calomel electrode. It is also important, for theaforementioned reasons, that the pH of the solution be acidic, in therange of 1.3 to 1.8 and preferably 1.5, at the time it is contacted withthe charcoal. Other than for these reasons, the adsorption efiiciencydoes not appear to depend on the pH value within this range. Theadjustment of degree of oxidation of the solution is achieved by theaeration step in which air is blown through the leach liquor, and alsoby the introduction of air directly into the adsorption tanks.

The charcoal used should be of the activated type and should have thefollowing characteristics. First, it should preferably be approximately8 x 20 mesh in size. Second, it must be of a type which will ad orbmolybdenum values. Third, it should be sufficiently hard that when it iscycled in the process it will not wear or fracture to a point where itmay no longer be separated by the relatively coarse screens used. Thereare now commercially available several charcoals which meet thesecriteria, such as Type CMO, 8 x 20 mesh, supplied by the PittsburghChemical Company. The thicker the pulp treated the more concentrated isthe molybdenum to be adsorbed, however, it should not be so thickas tointerfere with free circulation of the charcoal and slurry. The presentslurry is approximately 47% solids and has a specific gravity rangingfrom 1.35 to 1.45.

The loaded charcoal from the first screen is washed in Water and fed tothe charcoal stripping columns. The stripping operation has six stagesand is preferably carried out in a semi-continuous cycle operationutilizing six vertical columns of the type employed in ion exchangeoperations. When the loaded charcoal is loaded into one column itremains there until it is given the six stage treatment and is thenremoved. The timing of the cycle and staggering of stages is such thatcharcoal is being loaded and removed continuously, although each columnoperates on a batch basis. The six stages are as follows:

Stage 1.-The column is filled with loaded charcoal, the process takingabout sixty minutes.

Stage 2.The loaded charcoal is washed for about ten minutes with adownward flow of water.

Stage 3 .The wash water is drained, taking about fifty minutes.

Stage 4.-Ammoniation takes place using a gaseous mixture of from one totwo parts of air to one part NH (downward flow). About .8 to 1.2 andpreferably .87 to 1.0 pounds of NH are used per pound of molybdenumstripped. As little NI-I as is necessary should be used because ofrecovery costs. The air acts as a cooling agent and also assists thestripping operation by providing an oxidizing effect. It is believedthat the molybdenum compounds contain thionates, probably as adithionate ion (S O which will slowly be decomposed in later stages ofoperation to cause trouble. The air apparently oxidizes them tosulfates, which present no later extraction problems. The air alsooxidizes the molybdenum, which aids the stripping process. The amount ofair added in excess of a 1:1 ratio with NH will depend on thetemperature of the ammoniation reaction, and should be suflicient toprevent this temperature from exceeding the boiling point of thesolution. The ammonia reacts with the molybdenum in the solution to formammonium molybdate. Any iron sulfate carried along will be converted toferric hydroxide, a slimy substance which is carried out by the washwater.

Stage 5. Elution takes place with a downward flow of dionized water forabout sixty minutes.

Stage 6.The column is then emptied, which takes about twelve minutes.

Ammonia has been found to be a preferable stripping medium since it ismore economical than caustic. In addition, it is relatively easy torecover for re-use. Also, it and its resultant ammonium salts will burnoff with calcining to give molybdenum oxide. The pregnant solution whichleaves the charcoal stripping columns contains molybdenum as ammoniummolybdate (about 70 grams Mo/L), sulfur as ammonium sulfate (about 7grams S/L), and phosphorus as ammonium phosphate (about .7 grams P/L).The columns are operated at substantially atmospheric pressure and thesolution has a temperature of approximately 60 C. as a result of theheat of the ammoniation reaction. The actual temperature of the band ofammoniation occurring in this stage is just below the boiling point andtherefore additional heat is not required. Also, it has been found thatbetter stripping efiiciencies are obtained if the charcoal is moist,rather than dry. Approximately 98% of the molybdenum is stripped by thisprocess.

In the order of 20 pounds charcoal per ton of dry ore from the charcoalstripping columns is fed to a charcoal regeneration furnace where it isheated to 800 with steam for about one-half hour in the presence ofcombustion gases (CO and N This amount has been found to keep thecharcoal efficiency or greater as compared to virgin charcoal.Otherwise, the charcoal would become poisoned and adsorption would dropoff. The charcoal from the regeneration furnace is then mixed with theremaining charcoal flow from the charcoal stripping columns. At thispoint new charcoal to make up for any losses is also added to the systemand the combined charcoal flow is passed through a 1% sulfuric acidWash. H 50 is preferred because it is cheap and because it is the sameas that used in leaching. The acid wash removes any residual NH from thestripping operation which might otherwise react with the iron sulfate inthe ore slurry and form iron hydroxide, a slimy precipitate which wouldclog the charcoal. The acid-washed charcoal is then added to the secondseries of charcoal adsorption tanks to complete the charcoal cycle.Thus, in this series of adsorption tanks the freshest charcoal will bebrought into contact with the weakest slurry to thereby obtain some ofthe advantages of a counterfiow system, but with only one added screen.In addition, the afore described cocurrent recirculation of the slurrypermits high loading of the charcoal.

The ammonium molybdate solution from the stripping columns usuallycontains a small amount of phosphorus (the Mo/P ratio is in the order of:1). To remove this the ammonium molybdate solution is cooled to about20 to 25 C. and is fed to a precipitation tank where it is combined withmagnesium sulfate, which causes a precipitation of magnesium ammoniumphosphate, thus eliminating any phosphorous compounds picked up in thecharcoal from the ore. The pH of the solution should be above 8.6 and isabout 9.0 to 9.5. A 25% solution of magnesium sulfate is used in astoichiometric quantity suflicient to react with the amount ofphosphorous present, i.e., about 8 pounds of Epsom salt (MgSO -7H O) perpound of phosphorous. The solution is gently agitated for approximatelyeight hours. This allows time for an analysis of the solution todetermine if sufficient magnesium sulfate has been added. Only about 15to 30 minutes are necessary to actually precipitate. Thereafter, theprecipitated phosphorus compound, as well as any precipitated iron andother insoluble hydroxides which precipitated during stripping, arefiltered out of the solution. In addition, any other solid material willalso be filtered out of the solution. Two tanks may be used alternatelyso that while one is standing the other is being filled. They operate atatmospheric pressure. The filtered insolubles are then returned to theleach feed repulper at the beginning of the system, i.e., ahead of theleaching operation, for reprocessing to pick up any molybdenum valueswhich may remain in the solution. This is feasible because the charcoalpicks up only a minor portion of the phosphorous and therefore thephosphorous will not continue to build up.

The remaining filtrate solution contains ammonium molybdate, ammoniumsulfate, and free ammonia. The manner in which the molybdenum values areextracted from the solution does not form a part of the presentinvention and may be accomplished in any suitable manner. For example,the solution may be passed through a crystallizer in which ammoniumparamolybdate crystals will be formed. These crystals may then befiltered out and conveyed to a calciner for conversion to a finalproduct of molybdenum oxide of greater than technical grade. If ammoniumparamolybdate is desired as a final product it may be withdrawn from thesystem prior to the calcining operation.

As will be evident the present invention resides in the provision of anovel hydrometallurgical extraction process, and is not limited to theuse of any specific type of apparatus or equipment. Furthermore, in theabove example the amounts, ranges and so on are those which arepreferable for the extraction of ore of the type set forth. Oresdiffering slightly from the ores described herein may also be treated bythe present process, the only changes necessary being those which willbe readily apparent to one skilled in the art in light of the teachingsof the present disclosure.

Thus, there is disclosed in the above description and in the drawing anexample embodying the invention Which fully and effectively accomplishesthe objects thereof, however, it will be apparent that variations in thedetails set forth may be indulged in without departing from the sphereof the invention herein described or the scope of the appended claims.

What is claimed is:

1. Process for extracting molybdenum values from an ore containingoxidized molybdenum in association with iron, comprising: leaching theore with sulfuric acid and sulfur dioxide, desorbing the sulfur dioxide,adsorbing the molybdenum values with activated charcoal, and strippingthe molybdenum values from the loaded charcoal.

2. Process for extracting molybdenum values from an aqueous slurry ofore containing oxidized molybdenum in association with iron, comprising:leaching the ore with sulfuric acid and sulfur dioxide, desorbing thesulfur dioxide, adsorbing the molybdenum values with activated charcoal,and stripping the molybdenum values from the loaded charcoal.

3. Process for extracting molybdenum values from an ore containingoxidized molybdenum in association with iron, comprising: leaching theore with sulfuric acid and sulfur dioxide to form acid colloids of themolybdenum, desorbing the sulfur dioxide, adsorbing the molybdenum acidcolloids with activated charcoal, and stripping the molybdenum valuesfrom the loaded charcoal.

4. Process for extracting molybdenum values from an ore containingoxidized molybdenum in association with iron, comprising: leaching theore with sulfuric acid and sulfur dioxide, desorbing the sulfur dioxide,adsorbing the molybdenum values with activated charcoal, and strippingthe molybdenum values from the loaded charcoal with gaseous ammonia andair to form an ammonium salt of molybdenum.

5. Process for extracting molybdenum values from an ore containingoxidized molybdenum in association with iron, comprising: forming anaqueous slurry of the ore having a pulp density of 45% to 50%, leachingthe slurry with sulfuric acid and sulfur dioxide, desorbing the sulfurdioxide, adsorbing the molybdenum values with activated charcoal, andstripping the molybdenum values from the loaded charcoal.

6. Process for extracting molybdenum values from an ore containingoxidized molybdenum in association with iron, comprising: leaching theore with sulfuric acid and sulfur dioxide, desorbing the sulfur dioxide,oxidizing the leach liquor to an EMF level of 220 to 280 m.v. asmeasured by a platinum electrode with reference to a saturated calomelelectrode, adsorbing the molybdenum values with activated charcoal, andstripping the molybdenum values from the loaded charcoal.

7. Process as claimed in claim 6, wherein said oxidizing is performed byaerating the leach liquor.

8. Process for extracting molybdenum values from an aqueous slurry ofore containing oxidized molybdenum in association with iron, comprising:leaching the slurry with sulfuric acid and sulfur dioxide to form acidcolloids of molybdenum, desorbing the sulfur dioxide, adsorbing themolybdenum acid colloid with activated charcoal, and stripping themolybdenum values from the loaded charcoal with gaseous ammonia and airto form an ammonium salt of molybdenum.

9. Process for extracting molybdenum values from an aqueous slurry ofore containing oxidized molybdenum in association with iron, comprising:leaching the slurry with sulfuric acid and sulfur dioxide to form acidcolloids of the molybdenum, desorbing the sulfur dioxide, oxidizing theleach liquor to an level of 220 to 380 mv. as measured by a platinumelectrode with reference to a saturated calomel electrode, adsorbing themolybdenum acid colloid with activated charcoal, and stripping themolybdenum values from the loaded charcoal.

10. Process for extracting molybdenum values from an aqueous slurry ofore containing oxidized molybdenum in association with iron, comprising:leaching the slurry with sulfuric acid and sulfur dioxide to form acidcolloids of the molybdenum, desorbing the sulfur dioxide, oxidizing theleach liquor to an level of --220 to 380 mv. as measured by a platinumelectrode with reference to a saturated calomel electrode, adsorbing themolybdenum acid colloid with activated charcoal, and stripping themolybdenum values from the loaded charcoal with gaseous ammonia and airto form an ammonium salt of the molybdenum.

11. Process for extracting molybdenum values from an ore containingoxidized molybdenum in association With iron, comprising: forming anaqueous slurry of the ore having a pulp density of 45% to 50%, leachingthe slurry with sulfuric acid and sulfur dioxide to form acid colloidsof the molybdenum, desorbing the sulfur dioxide, aerating the leachliquor to oxidize it to an level of 220 to 380 mv. as measured by aplatinum electrode with reference to a saturated calomel electrode,adsorbing the molybdenum acid colloid with activated charcoal, andstripping the molybdenum values from the loaded charcoal with gaseousammonia and air to form an ammonium salt of the molybdenum.

12. Process for extracting molybdenum values from an ore containingoxidized molybdenum in association with iron, comprising: leaching theore, adsorbing the molybdenum values with activated charcoal, andstripping the molybdenum values fro-m the loaded charcoal with gaseousammonia and air to form an ammonium salt of the molybdenum.

13. Process for extracting molybdenum values from an ore containingoxidized molybdenum in association with iron, comprising: leaching theore, oxidizing the leach liquor to an level of 220 to 380 mv. asmeasured by a platinum electrode with reference to a saturated calomelelectrode, adsorbing the molybdenum values with activated charcoal, andstripping the molybdenum values from the loaded charcoal.

14. Process for extracting molybdenum values from an aqueous slurrycontaining oxidized molybdenum in association with iron, comprising:adding sufiicient sulfur dioxide to the slurry to leach the molybdenum,adding sufficient sulfuric acid to the leach liquor to establish andmaintain the pH thereof from about 1.0 to 1.3, desorbing the sulfurdioxide, oxidizing the leach liquor to an level of about -220 to 380 mv.as measured by a platinum electrode with reference to a saturatedcalomel electrode, adsorbing the molybdenumyalues with activatedcharcoal, and stripping the molybdenum values from the loaded charcoal.

15. Process for extracting molybdenum values from an aqueous slurrycontaining oxidized molybdenum in association with iron, comprising:adding sufficient sulfur dioxide to the slurry to leach the molybdenum,adding sufficient sulfuric acid to the leach liquor to establish andmaintain the pH thereof from about 1.0 to 1.3, desorbing the sulfurdioxide, oxidizing the leach liquor to an E.M.F. level of about 220 to380 mv. as measured by a platinum electrode with reference to asaturated calomel electrode, adsorbing the molybdenum values withactivated charcoal, and stripping the molybdenum values from the loadedcharcoal with gaseous ammonia and air to form ammonium molybdate.

16. Process for extracting molybdenum values from an aqueous slurrycontaining oxidized molybdenum in association with iron, comprising:adding suflicient sulfur dioxide to the slurry to leach the molybdenum,adding suflicient sulfuric acid to the leach liquor to maintain the pHthereof from about 1.0 to 1.3, desorbing the sulfur dioxide, oxidizingthe leach liquor to an level of about 250 to 300 mv. as measured by aplatinum electrode with reference to a saturated calomel electrode,adsorbing the molybdenum values with activated charcoal, and strippingthe molybdenum values from the loaded charcoal.

17. Process for extracting molybdenum values from an aqueous slurrycontaining oxidized molybdenum in association with iron,comprisingradding sufficient sulfur dioxide to the slurry to leach themolybdenum, adding sufficient sulfuric acid to the leach liquor tomaintain the pH thereof from about 1.0 to 1.3, desorbing the sulfurdioxide, oxidizing the leach liquor to an level of about 250 to 300 mv.as measured by a platinum electrode with reference to a saturatedcalomel electrode, adsorbing the molybdenum values with activatedcharcoal, and stripping the molybdenum values from the loaded charcoalwith gaseous ammonia and air to form ammonium molybdate.

18. Process for extracting molybdenum values from an aqueous slurrycontaining oxidized molybdenum in association with iron, comprising:adding sufficient sulfur dioxide to the slurry to bring the S ionconcentration up to about to grams per liter of solution for leachingthe molybdenum, adding suflicient sulfuric acid to the leach liquor tomaintain the pH thereof from about 1.0 to 1.3, desorbing the sulfurdioxide, oxidizing the leach liquor to an level of about 220 to 380 mv.as measured by a platinum electrode with reference to a saturatedcalomel electrode, adsorbing the molybdenum values with activatedcharcoal, and stripping the loaded charcoal.

19. Process for extracting molybdenum values from an aqueous slurrycontaining oxidized molybdenum in association with iron, comprising:adding suflicient sulfur dioxide to the slurry to bring the S0 ionconcentration up to about 10 to 15 grams per liter of solution forleaching the molybdenum, adding sufficient sulfuric acid to the leachliquor to maintain the pH thereof from about 1.0 to 1.3, desorbing thesulfur dioxide, oxidizing the leach liquor to an level of about -220 to380 mv. as measured by a platinum electrode with reference to asaturated calomel electrode, adsorbing the molybdenum values withactivated charcoal, and stripping the loaded charcoal with gaseousammonia and air to form ammonium molybdate.

20. Process for extracting molybdenum values from ores containingoxidized molybdenum in association with iron, comprising: forming anaqueous slurry of the ore, leaching the slurry with about 53 to 75pounds of 93% sulfuric acid and about 15 to 30 pounds of 100% sulfurdioxide per ton of ore, desorbing the sulfur dioxide, oxidizing theleach liquor to an level of about 220 to -380 mv. as measured by aplatinum electrode with reference to a saturated calomel electrode,adsorbing the molybdenum values with activated charcoal, and strippingthe molybdenum values from the loaded charcoal.

21. Process for extracting molybdenum values from ores containingoxidized molybdenum in association with iron, comprising: forming anaqueous slurry of the ore, leaching the slurry with about 53 to 75pounds of 93% surfuric acid and about 15 to 30 pounds of 100% sulfurdioxide per ton of ore, desorbing the sulfur dioxide, oxidizing theleach liquor to an level of about 220 to 380 mv. as measured by aplatinum electrode with reference to a saturated calomel electrode,adsorbing the molybdenum values with activated charcoal, and strippingthe molybdenum values from the loaded charcoal with gaseous ammonia andair to form ammonium molybdate.

22. Process of extracting molybdenum values from ores containingoxidized molybdenum in association with iron, comprising: forming anaqueous slurry of the ore having a pulp density of 45% to 50% solids,leaching the slurry with about 53 to 75 pounds of 93% sulfuric acid andabout 15 to 30 pounds of sulfur dioxide per ton of ore to form acidcolloids of the molybdenum, desorbing the sulfur dioxide, aerating theleach liquor to oxidize it to an level of about -250 to 300 mv. asmeasured by a platinum electrode with reference to a saturated calomelelectrode, adsorbing the molybdenum acid colloids with activatedcharcoal, and stripping the molybdenum values from the loaded charcoalwith gaseous ammonia and air to form ammonium molybdate.

23. Process as claimed in claim 22, wherein the stripping air to NHratio ranges from about 1:1 to 2:1.

24. Process as claimed in claim 23, wherein from about .8 to 1.2 poundsof NH are used per pound of molybdenum stripped.

25. Process for extracting metal values from an aqueous solution thereofin a slurry having a pulp density of from about 45% to 50% solids,comprising: feeding the slurry through a first series of adsorptiontanks concurrently with activated charcoal, feeding a fraction of theoutflow from the first series of tanks through a second series ofadsorption tanks, separating the loaded charcoal from the outflow of thesecond series of tanks and feeding it again through the first series oftanks, discharging the spent slurry from the second series of tanks outof the adsorption cycle, separating the slurry from the remainder of theoutflow from the first series of tanks and feeding it through the secondseries of tanks, stripping the metal values from the loaded charcoal inthe remainder of the outflow from the first series of tanks,regenerating a fraction of the stripped charcoal, and feeding theregenerated fraction of charcoal and the remaining unregeneratedstripped charcoal again through the second series of tanks.

26. Process for extracting metal values from an aqueous ore slurryhaving a pulp density of from about 45% to 50% solids, comprising:leaching the metal values from the ore in the slurry, feeding the slurrythrough a first series of adsorption tanks concurrently with activatedcharcoal, feeding a fraction of the outflow from the first series oftanks through a second series of adsorption tanks, separating the loadedcharcoal from the outflow of the second series of tanks and feeding itagain through the first series of tanks, discharging the spent slurryfrom the second series of tanks out of the adsorption cycle, separatingthe slurry from the remainder of the outflow from the first series oftanks and feeding it through the second series of tanks, stripping themetal values from the loaded charcoal in the remainder of the outflowfrom the first series of tanks, regenerating a fraction of the strippedcharcoal, and feeding the regenerated fraction of charcoal and theremaining unregenerated stripped charcoal again through the secondseries of tanks.

27. Process for extracting metal values from an aqueous ore slurryhaving a pulp density of from about 45 to 50% solids, comprising: addingsulfur dioxide and sulfuric acid to the slurry to leach the metalvalues, desorbing the sulfur dioxide, oxidizing the slurry to anoxidization level of about -220 to 380 mv. as measured by a platinumelectrode with reference to a saturated calomel electrode, feeding theslurry through a first series of adsorption tanks concurrently withactivated charcoal, feeding a fraction of the outflow from the firstseries of tanks through a second series of adsorption tanks, separatingthe loaded charcoal from the outflow of the second series of tanks andfeeding it again through the first series of tanks, discharging thespent slurry from the second series of tanks out of the adsorptioncycle, separating the slurry from the remainder of the outflow from thefirst series of tanks and feeding it through the second series of tanks,stripping the metal values from the loaded charcoal in the remainder ofthe outflow from the first series of tanks, regenerating a fraction ofthe stripped charcoal, and feeding the regenerated fraction of charcoaland the remaining unregenerated stripped charcoal again through thesecond series of tanks.

28. Process as claimed in claim 27, wherein stripping is accomplishedusing ammonia and air.

29. Process for extracting molybdenum values from ores containingoxidized molybdenum in association with iron, comprising: leaching theore with sulfuric acid and sulfur dioxide, desorbing the sulfur dioxide,adsorbing the molybdenum values with activated charcoal, and strippingthe molybdenum values from the loaded charcoal with gaseous ammonia andair to form an ammonium salt of the molybdenum, the air to ammonia ratiobeing from about 1:1 to 2:1.

30. Process as claimed in 29, wherein from about .8 to 1.2 pounds ofammonia are used per pound of metal stripped.

31. Process for extracting molybdenum values from ores containingoxidized molybdenum in association with iron, comprising: leaching theore with sulfuric acid and sulfur dioxide, desorbing the sulfur dioxide,feeding the leach liquor to adsorption tanks where the molybdenum valuesare extracted by activated charcoal, adding air to the absorption tanks,and stripping the molybdenum values from the loaded charcoal.

32. Process for extracting molybdenum values from the tailings frompreliminarily flotation treated natural molybdenum containing ore,comprising: leaching the ore with sulfuric acid and sulfur dioxide,desorbing the sulfur dioxide, absorbing the molybdenum values withactivated charcoal, and stripping the molybdenum values from the loadedcharcoal.

No references cited.

DAVID L. RECK, Primary Examiner.

N. F. MARKVA, Assistant Examiner.

1. PROCESS FOR EXTRACTING MOLYBDENUM VALUES FROM AN ORE CONTAININGOXIDIZED MOLYBDENUM IN ASSOCIATION WITH IRON, COMPRISING: LEACHING THEORE WITH SULFURIC ACID AND SULFUR DIOXIDE, DESORBING THE SULFUR DIOXIDE,ADSORBING THE MOLYBDENUM VALUES WITH ACTIVATED CHARCOAL, AND STRIPPINGTHE MOLYBDENUM VALUES FROM THE LOADED CHARCOAL.